Generally a hearing aid system according to the invention is understood as meaning any system which provides an output signal that can be perceived as an acoustic signal by a user or contributes to providing such an output signal and which has means adapted to compensate for an individual hearing loss of the user or contribute to compensating for the hearing loss. These systems may comprise hearing aids which can be worn on the body or on the head, in particular on or in the ear, and can be fully or partially implanted. However, those devices, whose main aim is not to compensate for a hearing loss, may also be considered a hearing aid system, for example consumer electronic devices (televisions, hi-fi systems, mobile phones, MP3 players etc.) provided they have, however, measures for compensating for an individual hearing loss.
Prior to use, the hearing aid is adjusted by a hearing aid fitter according to a prescription. The prescription is based on a hearing test, resulting in a so-called audiogram, of the performance of the hearing-impaired user's unaided hearing. The prescription is developed to reach a setting where the hearing aid will alleviate a hearing loss by amplifying sound at frequencies in those parts of the audible frequency range where the user suffers a hearing deficit.
In a traditional hearing aid fitting, the hearing aid user visits an office of a hearing aid fitter, and the user's hearing aids are adjusted using the fitting equipment that the hearing aid fitter has in his office. Typically the fitting equipment comprises a computer capable of executing the relevant hearing aid programming software and a programming device adapted to provide a link between the computer and the hearing aid.
Within the present context a hearing aid can be understood as a small, battery-powered, microelectronic device designed to be worn behind or in the human ear by a hearing-impaired user. A hearing aid comprises one or more microphones, a battery, a microelectronic circuit comprising a signal processor, an amplifier, and an acoustic output transducer. The signal processor is preferably a digital signal processor. The hearing aid is enclosed in a casing suitable for fitting behind or in a human ear.
The mechanical design of hearing aids has developed into a number of general categories. As the name suggests, Behind-The-Ear (BTE) hearing aids are worn behind the ear. To be more precise, an electronics unit comprising a housing containing the major electronics parts thereof is worn behind the ear. An earpiece for emitting sound to the hearing aid user is worn in the ear, e.g. in the concha or the ear canal. In a traditional BTE hearing aid, a sound tube is used to convey sound from the output transducer, which in hearing aid terminology is normally referred to as the receiver, located in the housing of the electronics unit and to the ear canal. In some modern types of hearing aids a conducting member comprising electrical conductors conveys an electric signal from the housing and to a receiver placed in the earpiece in the ear. Such hearing aids are commonly referred to as Receiver-In-The-Ear (RITE) hearing aids. In a specific type of RITE hearing aids the receiver is placed inside the ear canal. This category is sometimes referred to as Receiver-In-Canal (RIC) hearing aids.
In-The-Ear (ITE) hearing aids are designed for placement in the ear, normally in the funnel-shaped outer part of the ear canal. In a specific type of ITE hearing aids the hearing aid is placed substantially inside the ear canal. This category is sometimes referred to as Completely-In-Canal (CIC) hearing aids. This type of hearing aid requires an especially compact design in order to allow it to be arranged in the ear canal, while accommodating the components necessary for operation of the hearing aid.
Within the present context a hearing aid system may comprise a single hearing aid (a so called monaural hearing aid system) or comprise two hearing aids, one for each ear of the hearing aid user (a so called binaural hearing aid system). Furthermore the hearing aid system may comprise an external device, such as a smart phone having software applications adapted to interact with other devices of the hearing aid system. Thus within the present context the term “hearing aid system device” may denote a hearing aid or an external device.
Contemporary digital hearing aids incorporate a digital signal processor for processing audio signals from the microphone into electrical signals suitable for driving the acoustic output transducer according to the prescription. In order to save space and improve efficiency, some digital hearing aid processors provide a digital output signal to drive the acoustic output transducer directly without performing a digital-to-analog conversion of the output signal. If the digital signal is delivered to the acoustic output transducer directly as a digital bit stream with a sufficiently high frequency, the coil of the acoustic output transducer performs the duty as a low-pass filter, allowing only frequencies below e.g. 15-20 kHz to be reproduced by the acoustic output transducer. The digital output signal is preferably a pulse-width modulated signal, a sigma-delta modulated signal, or a combination thereof.
An H-bridge is an electronic circuit for controlling inductive loads such as electric motors or loudspeakers. It operates by controlling the direction of a flow of current through a load connected between the output terminals of the H-bridge by opening and closing a set of electronic switches present in the H-bridge. The switches may preferably be embodied as semiconductor switching elements such as Bipolar Junction Transistors (BJT) or Metal Oxide Semiconductor Field Effect Transistors (MOSFET). This operating principle permits a direct digital drive output stage to be employed in order to enable a suitably conditioned digital signal to drive a loudspeaker directly, thus eliminating the need for a dedicated digital-to-analog converter and at the same time reducing the power requirements for the output stage.
The present invention, in particular, relates to hearing aid systems comprising an ear canal part prepared for being arranged in the ear canal of a hearing aid user and wherein the ear canal part has at least one sound output opening or sound outlet provided with an ear wax guard. In traditional BTE hearing aids the sound output opening is connected to the receiver with a sound tube. For RITE, RIC, ITE and CIC hearing aids a short tubing (may also be denoted a sound bore) is normally used to convey the sound from the receiver and to the sound output opening.
It is a well-known problem that inside the ear canal the sound output opening is exposed to contamination with cerumen or ear wax which may lead to congestion of the sound output with consequently reduced sound reproduction. At worst, there may be a risk for the ear wax to enter the ear canal part and result in damage to the electrical components of the hearing aid such as the hearing aid receiver. In any case, a reduced level of the sound provided by the hearing aid system may have the consequence that the hearing aid system is not worn by a user or that a user having the hearing aid system on trial selects not to purchase it.
However, congestion of the sound output need not be due to ear wax it may also be the result of water condensation in the sound conduit between the receiver and the sound output opening.
In order to avoid ear wax from the human ear canal to enter through this sound output opening, an ear wax guard is usually applied. Such an ear wax guard is known from e.g. EP-B1-1097606. Ear wax guards are exchangeable and need to be replaced on a regular basis in order not to have the sound outlet blocked by ear wax. The time between changes of the ear wax guard varies between users, because the amount and characteristics of ear wax produced may differ significantly from person to person.
However as a consequence of the very small dimensions, the sound outlet typically having a diameter of about 1 mm, the insertion and removal of the ear wax guard is a rather difficult operation, especially for weak-sighted and elderly hearing aid users. As a consequence, it often happens that ear wax guards are not replaced as often as they should whereby the risk of ear wax entering the ear canal part is increased, hereby also increasing the risk of damaging especially the hearing aid receiver or increasing the risk of the hearing aid system providing sound at a significantly reduced level.
EP-B1-2039216 discloses a method for monitoring a hearing device comprising an electro-acoustical output transducer worn at or in a user's ear or in a user's ear canal, wherein the electrical impedance of the output transducer is measured and analyzed, whereby the status of the output transducer and/or of an acoustical system cooperating with the output transducer, such as a tubing of a BTE hearing device, may be evaluated in a simple and efficient manner. Thereby it is enabled to automatically and immediately recognize when the output transducer or an acoustical system cooperating with the output transducer is blocked by ear wax or when the output transducer is damaged.
EP-B1-2039216 more specifically discloses a method wherein a reference receiver impedance is initially measured at a resonance frequency for the receiver, and wax congestion is subsequently evaluated based on comparing additional measurements of the receiver impedance at said resonance frequency with the reference receiver impedance.
This method is characterized in that the difference between the additionally measured receiver impedances and the reference receiver impedance in addition to the change of the receiver impedance also depends on the amplitude of the signal used to measure the receiver impedance (in the following also denoted measurement signal) and depends on the magnitude of a measurement resistor applied in the receiver impedance measurement circuitry.
However, the amplitude of the measurement signal will typically drift with time and the specific environmental conditions because the source of the measurement signal will most likely be the hearing aid battery, which typically cannot be trusted to provide a constant voltage output over time. The method disclosed in EP-B1-2039216 does not describe how to compensate for possible variability of the battery voltage.
The method disclosed in EP-B1-2039216 is further disadvantageous in that the use of only one measurement resistor does not allow the sensitivity of a measured voltage that represents changes in the receiver impedance to be optimized for a broad range of different hearing aid receiver impedances, which is disadvantageous since most contemporary hearing aids may be fitted with several different types of receivers having reference impedances that may vary significantly. Typically the receiver type is selected based on the severity of the individual hearing loss and the size of the individual ear canal.
It is a feature of the present invention to provide a method of operating a hearing aid system that improves detection of possible mechanical congestion of a hearing aid due to e.g. ear wax or water.
It is another feature of the present invention to provide a hearing aid system adapted to carry out said improved method.